Several methods have been reported for producing and screening large libraries to identify compounds having specific affinity for a target. These methods include the phage-display method in which randomized peptides are If displayed from phage and screened by affinity chromatography to an immobilized receptor. See, e.g., Dower et al., WO 91/17271; McCafferty et al., WO 92/01047; Ladner, U.S. Pat. No. 5,223,409 (incorporated by reference in their entirety for all purposes). In another approach, combinatorial libraries of polymers immobilized on a chip are synthesized using photolithography. See, e.g., U.S. Pat. No. 5,143,854; WO 90/15070 and WO 92/10092. The immobilized polymers are contacted with a labelled receptor and scanned for label to identify polymers binding to the receptor.
A general, and particularly useful, method for synthesizing and screening large libraries of compounds is the encoded synthetic library method (ESL) of Dower et al. In this method, the different compounds in the library are usually synthesized attached to separate supports (e.g., beads) by stepwise addition of the various components of the compounds in several rounds of coupling. A round of coupling can be performed by apportioning the supports between different reaction vessels and adding a different component to the supports in the different reaction vessels. The particular component added in a reaction vessel can be recorded by the addition of a tag component to the support at a second site. After each round of synthesis, supports from the same reaction vessel can be apportioned between different reaction vessels and/or pooled with supports from another reaction vessel in the next round of synthesis. In any, and usually in all rounds of synthesis, the component added to the support can be recorded by addition of a further tag component at a second site of the support. After several rounds of synthesis, a large library of different compounds is produced in which the identities of compounds are encoded in tags attached to the respective supports bearing the compounds. The library can be screened for binding to a target. Supports bearing compounds having a specific affinity for the target are isolated, and the identity of such compounds can be determined by decoding the tags.
All of the above methods have proved successful in isolating compounds having specific affinity for a target of interest. For example, the methods have been used to isolate compounds that bind to a cellular receptor for use as antagonists of receptor-ligand interactions. However, the repertoire of compounds that can be identified by some of the above methods is somewhat limited by the fact that compounds are screened in a tethered format. Furthermore, existing screening methods generally have not been used to distinguish between compounds that merely bind to a receptor, and compounds that are capable of transducing a biological signal through the receptor. The latter compounds are expected to have particularly useful properties, such as the capacity to agonize normal ligand-receptor interactions. These properties can be exploited in many applications such as stimulation of cell or tissue growth, and enzyme, growth factor or hormone replacement therapy.
The present invention provides methods for screening compounds for capacity to transduce a signal through a cellular receptor, thereby allowing the isolation of novel pharmaceuticals.